Fabrication of conductive electrodes with molecular sized separations is required for the electrical characterization of single molecules. Electrical characterization of single molecules in turn is essential for the development of single molecular electronic devices, including chemical and biological sensors. Several methods have been demonstrated to fabricate electrodes having gap dimensions measured in units or tens of nanometers (which are also referred to as “nano-gap electrodes”). The methods include: fabrication of thin wires comprising mechanical break junctions; electromigration of metal to cause a break in a wire; electrochemical deposition techniques on planar substrates; shadow evaporation of metals onto planar substrates; focused ion beam etching of metallic structures on planar substrates; and e-beam lithography of metallic structure on planar substrates. Most of these approaches are, however, not easily controllable and suffer poor reproducibility, low yield, and low throughput. The e-beam lithography method is relatively controllable and reproducible. However well-controlled creation of <10 nm gap electrodes was achieved only by using elaborate e-beam overlapping and overexposure lithography techniques. The focused ion beam method can generate <10 nm gap electrodes using Ti mask patterns with focused ion beam etching. However focused ion beam systems are not readily available due to the extremely high cost of the apparatus used to generate such beams. Furthermore, all these previously demonstrated methods are not suitable for producing highly dense nanoelectrode arrays that are electrically addressable for chemical and biological sensor applications.
There is a need for highly dense nano-gap electrode array structures that are electrically addressable for chemical and biological sensor applications and for methods of fabricating such nano-gap electrode arrays.